High-speed wireless data communication networks form the basis for cellular and mobile communications, and have become increasingly important in expanding access and availability to the rich functions, features, and capabilities that are associated with smart phones and connected tablet devices. High-speed data communication networks evolved through second generation (2G) wireless networks and third generation (3G) wireless networks into the current fourth generation (4G) wireless networks such as Long Term Evolution (LTE) and LTE-Advanced (LTE-A) networks and Wireless Metropolitan Area Networks (MAN)-Advanced networks. In the future, fifth generation (5G) networks such as Cloud-Radio Access Network (C-RAN), Coordinated Multi Point (CoMP), and future 3rd Generation Partnership Project (3GPP) will add enhanced capabilities to support a broad range of communication, media, and computing capabilities as will be needed for the features of the future.
The later generation (4G and 5G) wireless network technologies have adopted Multiple-Input and Multiple-Output (MIMO) transmission technology that uses multiple transmit and receive antennas to exploit multipath signal propagation, in order to increase bandwidth and improve reliability. MIMO technology provides the transmission of a common set of information over multiple radio channels in order to take advantage of the variations in signal paths between the transmit and receive antennas to improve the transmission of the information. For example, the LTE (4G) network technology calls for up to eight antennas. The upcoming 4G releases and next generation 5G network technologies under development will utilize Massive-MIMO arrays of 16, 24, and more antennas. One challenge created by the use of Massive-MIMO is the need to equalize the signals received from the individual antennas to account for differences in the phase shift and loss associated with the different channels, especially as the number of antennas in the MIMO array increases.
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